Effect of abnormal structure on creep strength of long-term used 9Cr steel welded joint

• Published in: Materials at high temperatures Vol. 39; no. 6; pp. 578 - 589
• Main Authors: Zhang, Shengde, Tokunaga, Hayato, Kanai, Masayuki, Lin, Shan, Yaguchi, Masatsugu, Tamura, Koji, Minami, Yusuke
• Format: Journal Article
• Language: English
• Published: Taylor & Francis 02.11.2022
• Subjects: 9Cr ferritic steels; abnormal structure; creep; life assessment; microstructure; USC power plant; welded joint
• ISSN: 0960-3409; 1878-6413
• DOI: 10.1080/09603409.2022.2058235

Microstructural characteristics of abnormal structure in long-term used Gr.91 steel weldments and its effect on creep strength of welded joint are presented. The abnormal structure is defined as a structure in which the hardness is clearly lower than that in the normal region, and the grain is coarsened. Creep strength of the abnormal structure is significantly lower than that of normal weld metal. There is little effect of abnormal structure formed in the HAZ on creep life of standard welded joint specimensr. In case of abnormal structure formed in the weld metal, times to creep rupture of standard specimens are shorter than those of specimens without abnormal structure. Full-thickness welded joint specimen consisting more than half abnormal structure in the weld metal ruptured at the weld metal before the HAZ. Time to creep rupture decreased with increasing the abnormal structure ratio in thickness direction.